Lead markers are sewn in place within the individual tendons of the Achilles group in dogs. Bone screws in the tibia serve as a length standard in the same plane as the tendon. The animal runs on a treadmill in front of an x-ray cine camera, which operates at 200 frames/sec. After the running experiments, the individual tendons are removed and stretched in front of the x-ray cine camera again. In this way, the tendons are calibrated as force transducers, and it is possible to return to the running films to calculate individual muscle force, muscle length, tendon strain energy, and other mechanical parameters of the muscle and tendon during the stride cycle.